News Release

As Montana Snowpack Transitions Into Spring, Runoff Should Be Monitored

BOZEMAN, Mont., May 7, 2014–Data from the USDA Natural Resources Conservation Service (NRCS) SNOTEL (SnoTelemetry) sites show Montana’s April snowfall did not match the well above average precipitation experienced during February and March, but because Montana has not yet seen a major shift in weather patterns, snowmelt has been delayed and basin percentages of normal remain high.

Data shows most basins in the state exhibited peak snow water equivalent during the beginning and middle part of April, while some basins in southwest Montana and along the Continental Divide exhibited peaks at the end of the month. According to Lucas Zukiewicz, NRCS hydrologist, some snowmelt has occurred at lower to mid elevations, but higher elevations in the basins have seen little melt during the month, delaying when the bulk of snowmelt runoff enters river systems. “Assuming normal climatic conditions in the upcoming weeks, more advanced melt rates should begin to occur as days get longer with more solar influence and temperatures get warmer," Zukiewicz said.

Statewide SNOTEL and snow course data reported 155 percent of normal for May 1 and 149 percent of last year at this time. The Bitterroot River Basin currently has the highest basin percentage of normal in the state, indicating 188 percent of normal for May 1 and 199 percent of last year at this time. “Worth noting this month are the Missouri Mainstem, Tongue, and Powder River basins which reported the highest daily snow water equivalent values (SWE) since 1981,” Zukiewicz said. “However, the 2014 peak snow water equivalent did not surpass those recorded 1997 and 2011.”

Snow Water Content

River Basin

May 1 Percent of Median

Percent of Last Year

Columbia

159

148

Kootenai, Montana

145

126

Flathead, Montana

156

138

Upper Clark Fork

162

170

Bitterroot

188

199

Lower Clark Fork

164

138

Missouri

150

153

Missouri Headwaters

142

149

- Jefferson

143

159

- Madison

135

141

- Gallatin

148

142

Missouri Mainstem

172

164

- Headwaters Mainstem

180

186

- Smith-Judith-Musselshell

158

154

- Sun-Teton-Marias

178

160

- Milk (Bearpaw Mountains)

0

0

St. Mary

138

116

St. Mary and Milk

136

115

Yellowstone

157

153

Upper Yellowstone

166

166

Lower Yellowstone

149

144

Statewide

155

149

Zukiewicz said if snowmelt continues to be delayed in the mountains, the basin percentages of normal will continue to increase. “This time of year the daily normal value that we compare current snow water equivalent values to is decreasing as it generally represents a melting snowpack. If basin snow water equivalent decreases at a slower rate than the daily normal, or increases while the normal decreases, the basin percentages climb. Since the peak may have been observed in many of the basins, the basin percentages are indicating that there is a substantial amount of snow water left in the mountains for runoff this spring,” he said.

While April precipitation varied across the state, the statewide precipitation for April was slightly below average at 93 percent. The far western basins along the Idaho border and central part of Montana received well below average precipitation for the month. The overall water year-to-date precipitation totals since Oct. 1 still reflect above average precipitation (to date) in most basins. The statewide precipitation is currently 116 percent of average, and 115 percent of last year at this time.

Streamflow Forecasts

Streamflow prospects continue to be well above average in most parts of the state. Statewide streamflow forecasts indicate 146 percent of the average May-July flows, and 152 percent of what was experienced last year. The Smith-Judith-Musselshell combined river basin continues to have the highest percentage of average May-July flows using the 50 percent exceedance forecast at 182 percent of average. The extreme headwaters of the Jefferson River basin continue to have the lowest forecasts in the state indicating 72 percent of average May-July flows for Lima Reservoir inflow and 80 percent for Clark Canyon inflow. For greater detail on spring runoff forecasts, consult the May 1 Water Supply Outlook Report.

Below are the averaged River Basin streamflow forecasts for the period May 1 through July 31. THESE FORECASTS ASSUME NEAR NORMAL MOISTURE AND RUNOFF CONDITIONS JANUARY THROUGH JULY.